Computed tomography (CT) is a medical imaging tool that gives high-resolution 3D tomography information of anatomic structures based on different X-ray absorption of tissues and lesions. Iodinated compounds with high X-ray absorption coefficient have been used for CT contrast agents for decades. Recently, nanoparticle-based CT contrast agents (e.g., polymer-coated bismuth sulfide nanoparticles and PEG-coated gold nanoparticles) have been designed to provide better contrast effect than iodinated compound-based contrast agents.
Magnetic resonance imaging (MRI), on the other hand, provides unsurpassed 3D soft tissue details and functional information of lesions. Due to its non-ionizing radiation, high sensitivity to distribution of water and other biomolecules, MRI has been applied in clinic for diagnosis of many diseases. Gadolinium (Gd3+)-based T1 contrast agents and superparamagnetic iron oxide nanoparticle-based T2 contrast agents are two major types of MRI contrast agents.
Only a few contrast agents with dual imaging contrast effect have been developed, e.g., Gd-G8 dendrimer and Gd chelated gold nanoparticles. See C. A. S. Regino, et al., Contrast Media & Molecular Imaging, 2008, 3, 2-8, C. Alric, et al., J. Am. Chem. Soc., 2008, 130, 5908-5915. There is a need to develop new contrast agents that can be used in both CT and MR imaging.